See our 5 day blastocyst transfer success rates; See our overall IVF success rates. 4BB ’4bb blastocyst’ - Infertility egg donation Grading Blastocyst Stage embryos (Day 5, Day 6 embryos) :. Expanded Blastocysts generally will be 4AA, 4AB, 4BB...... Premature ovarian failure success story Read more... blastocyst quality 4bb; day 5 hatching blastocyst 4bb; day 6 4bb blastocyst fet; chances of 4bb blastocyst success; 4bb blastocyst success rates lab I am wondering if anyone has had success with 4BB's and if so, any. it! your transfer is the same day as mine! i had 3 blastocyst transferred yesterday. graded 4bb.